The present invention relates to a multi-cavity klystron, more particularly to a multi-cavity klystron of the class wherein an electron beam is made to travel along a straight path in the cavity and the resonance frequency of each cavity resonator which is arranged along the path of electron beam is able to be preset.
The multi-cavity klystron generally comprises an electron gun which is adapted to produce an electron beam, a collector means for catching electrons emitted, and a high frequency circuit having a plurality of cavity resonators for making the electron beam interact with micro waves input, all the constituents above are arranged in one axis and said high frequency circuit further comprises a plurality of cavity resonators. With this construction, a high voltage is produced in the intermediately located cavity resonator due to the modulated electron flow formed in the cavity in front, thereby the electron flow is further modulated in its velocity. As a result, the operating frequency and gain is largely improved as compared with the two-cavity type klystron.
Generally, as mentioned above, the klystron is provided with means capable to changing the resonance frequency of each cavity resonator so as to change the band characteristics and usable channels. In principle, for changing the resonance frequency, there would be considered means adopting the following three methods.
(1) The C-tuning method in which capacitance of the cavity is adjusted,
(2) The L-tuning method in which inductance of the cavity is adjusted, and
(3) The combination of the above two methods.
In a conventional type means for adjusting the resonance frequency, there are provided independent adjusting means each of which follows either one of the above adjusting method, and upon adjustment, each means is adjusted by an instrument proper thereto for obtaining a necessary characteristics thereof. The adjustment above, however, would result in a very complicated and a time consuming work in general, unless performed by one trained well in that field.
For the purpose of solving difficulty as described above, a preset tuner mechanism has been proposed, which not only one trained well but also a beginner can be performed a suitable adjustment in a short time without a sophisticated measuring instrument. In this mechanism, there is included means which can specify in advance a particular resonance frequency, i.e. channel and is manually and simply set a desired resonance frequency. For instance, a multi-cavity micro wave gang-operation tuner has already been disclosed in U.S. Pat. No. 3,617,799 patented Nov. 2, 1971. At present, however, there is used the same type means as described above, or the one that is modified therefrom but keeping the same principle as the above. The klystron having such a preset tuner comprises in general movable elements provided in each cavity resonator for changing the resonance frequency, tuning rods coupled with each movable element, a cam which contacts with the other end of each tuning rod and selectively determine the position of the element in the cavity resonator, a cam gear with said cam, which is used for selecting a channel, a channel selection knob for rotating said cam gear, a control means for engaging or disengaging each tuning rod with or from said cam, and a knob for controlling said control means. Each gear is constructed in such a way that it can rotate co-operatively or jointly by the operation of the channel selecting knob.
When the resonance frequency is needed to change, the control knob is firstly operated so as to disengage the tuning rod from the knob by the control means, and then the channel selection knob is operated so as to face the cam corresponding to a predetermined resonance frequency to the other end of each tuning rod, and further, in keeping this condition, each control knob is reversely operated so as to contact each tuning rod with each cam. By this operation, the position of each movable element in each cavity resonator is determined, thereby the electrical variables in the cavity resonator such as capacitance, inductance, or the both in the resonator coming to have predetermined values and a micro wave energy with a desired frequency characteristics being output.
In such a preset tuner mechanism as described above, however, a preset value is determined by the cam that is provided along the periphery of the cam gear. In other words, the preset value is determined by using the mechanical memory means, so that the following drawbacks will be often observed.
(1) In view of the structure of the multi-cavity klystron, the cam gear provided corresponding to each cavity resonator is restricted in its size, so that the number of cams to be mounted thereon is to be naturally limited. For instance, in the klystron five cavities of 6 GHz, six cams are maximum to be accepted by the cam gear, which make use of six channels available.
(2) When an operating frequency of the klystron becomes very high, the size of the cavity of the klystron becomes essentially small so that the size of the preset tuner mechanism is also required to be smaller. In the conventional preset tuner mechanism, however, various parts as described above have to be included, so that a considerably large space is required for accomodating them. Accordingly, a limitation is imposed for making the mechanism small, and even if it should be possible to miniaturize parts for the mechanism installing or assembling the same would become difficult. As described above, there must be considered a limitation for the size of the mechanism in view of the operating frequency of the klystron. On one hand, there is another demand that channels are to be more increased in their number, and there is still another demand that there should be provided a preset tuner mechanism which can be installed in a high frequency, operated klystron.